Field of the Invention
The invention relates to a delivery of a sheet-processing printing machine having grippers which revolve during operation and transfer the processed sheets in a conveying direction to a sheet brake.
The published German Patent Document DE 44 35 988 A1 discloses suction devices revolving at a variable speed, which grip the sheets, respectively, transported via the revolving grippers, in a region of the sheets that is adjacent to the trailing edge, at an instant of time at which the speed of the suction devices coincides with the processing speed of the printing machine. Thereafter, the grippers release the respective sheet gripped by the suction devices and the suction devices are braked to a reduced revolving speed at which they, for their part, finally release the sheets for the purpose of forming a sheet pile.
This process takes place without disruption only when, in particular, assurance is provided that the region of a respective sheet that is to be gripped by the suction devices and is adjacent to the trailing edge of the sheets is guided as far as possible so that it does not flutter about, in particular, at that instant of time at which the suction devices, respectively, are to grip such a region.
Flutter-free guidance of printed sheets in a delivery is also an important precondition for achieving satisfactory printed products with respect to avoiding the smearing or smudging of a printed image applied to the sheets. Efforts to satisfy this precondition can be gathered from the prior art, in particular, from the published German Patent Document DE 42 39 561 A1. This document proposes to avoid whiplash-like movements of the trailing sheet edge by providing a guide surface disposed parallel to the path along which the grippers transport a respective sheet, with positive guidance of the leading edge of the respective sheet, as viewed in the conveying direction, and which can be moved continuously in the conveying direction of the grippers at sheet-conveying speed, the directing surface being formed by a suction-belt arrangement which secures a region of a respective sheet that is adjacent to the trailing edge of the sheet, the region being attached by suction in the process, with the result that a respective sheet is subjected to positive guidance not just in the region of the leading edge thereof, but more-or-less in the region of the trailing edge thereof, as well.